The present invention relates to medical equipment, techniques and procedures, and more particularly, to the circulation and recovery of blood during and immediately following heart bypass and similar surgery involving a cardiopulmonary bypass circuit (CPB) or more generally, an extracorporeal blood circuit (ECC).
A persistent dilemma is faced thousands of times each day worldwide, of how to handle the volume of a patient's blood in the ECC after the surgical procedure has been completed and the patient is disconnected from the circuit.
One option is to transfuse the volume in the circuit to the patient, in the manner of a blood transfusion, without compromising the integrity of the bypass system. It should be appreciated that the circuit includes a crystalloid priming fluid which is necessary to initiate the pumping of the circuit. Therefore, transfusion of the content of the circuit would include transfusion of the priming solution which, by the end of the surgery, has been fully mixed with the patient's own blood. The hematocrit concentration is therefore low, i.e., approximately 18-25%. Although some such diluted blood can be transfused to the patient, a relatively large fraction of the volume of the circuit is not transfused, because this volume is needed to maintain the integrity of the circuit in the event full bypass is to be resumed. Also the patient's physiology can only accommodate a finite amount of volume before circulatory overload or TACO is exhibited with organ edema and dysfunction.
Alternatively, the content of the ECC circuit can be transferred to sterile blood bags, for a possible re-transfusion to the patient either in or out of the operating room. This option also suffers from a large amount of volume with the dilution of important blood components and the need to keep a substantial fraction of the diluted blood in the circuit to maintain circuit integrity.
Yet a third option, is to chase all the volume in the ECC circuit with a crystalloid solution to a so-called “cell washer”, where the fluid volume is separated into red blood cells and effluent. Although the red blood cells are saved, the effluent is deemed waste and therefore discarded, yet the effluent contains many desirable constituents of whole blood, such as plasma, platelets, clotting factors, albumin, proteins, etc.
Finally, the most straight-forward option is to seal or drain and discard the content of the ECC circuit. This is common in pediatric open heart cases, but benefits neither the patient nor anyone else, and presents a significant disposal problem to the perfusionist (i.e., the operator of the heart/lung machine), who must clean up and discard this wasted volume.
Because in the foregoing options, the patient cannot receive his own entire blood volume from the circuit immediately following cardiac, thoracic, or vascular procedures, if the need for additional blood arises, the only available source is from previously stored blood bags. If the patient gave blood prior to surgery, which is rare, then the patient could receive so-called autologous blood. Most often, however, such additional blood or blood products would be provided from a dwindling and precarious blood bank supply, which originated from an allogeneic (unknown) donor. Transfusing such blood can arouse anxiety and create problems including hemolytic reactions, immunological reactions blood viruses; vCJD or Prion's disease (BSE) and Trali or TACO. Human error can occur when mistakes are made by giving non-compatible or mislabeled blood products. Artificial blood substitutes or HBOC's can be used, but these are limited to carrying only oxygen, have a short half-life and do not compare favorably to the miraculous abilities of the patient's own blood. Lastly, there is also a small population of patients that completely refuse any foreign blood or blood products of any kind, due for example, to religious beliefs.
Because of these reasons, the need exists to reduce allogeneic blood use and strive for “bloodfree surgery” and the growing movement towards blood management.
Significant improvements toward achieving this goal have already been implemented using the Hemobag® techniques described in the present inventor's U.S. Pat. Nos. 5,928,178; 6,398,751; 7,033,334; and 7,402,278, the entire disclosures of which are hereby incorporated by reference. A substantial volume of concentrated whole blood can be quickly and easily recovered from the ECC immediately following, i.e., cardiac, thoracic, or vascular surgery. Most of the blood in the ECC flows into a blood reservoir, preferably a dedicated blood bag, and hemoconcentrated in the blood reservoir while connected in a sub circuit of the ECC.
In addition to the recovery of a patient's blood following surgery, a related concern is the management of the fluid or volume in the ECC and in the patient during surgery. The volume of fluid circulated to the patient during surgery over the course of several hours must be varied to correspond with the particular stages in the surgery and the patient's physiology. Make-up fluid or volume (crystalloid, colloid or blood product) is required when the overall need or blood concentration in the ECC and the patient needs correction for stabilization. This large amount of diluted blood increases the time necessary for recovery of the patient's whole blood after surgery.
Extracorporeal circuits can be necessary after surgery, for example in the critical intensive care unit (ICU) where the patient relies on the ECC for a period of days rather than hours (ECMO or VADS). The concentration of blood in the patient and the circuit, and the total volume of fluid in the patient plus the circuit can vary considerably, and it is important that the fluid volume management be closely monitored.
Presently, fluid management is rather varied and implemented by opening and closing clamps into and out of the venous reservoir of the ECC. Regardless of any other components that may be fluidly aligned, when the venous reservoir is fluidly connected in series in the fluid path along the cannula line from the patient and the cannula line to the patient, the venous reservoir acts imprecisely as an in-line accumulator of fluid or volume when the flow to the patient is to be decreased and as a source of fluid volume when flow to the patient is to be restored or increased.